There analogy is not good, but I would also assume that lockheed won a competitive bidding process to get the contract as well. They promised to build it at a certain price and in a certain time.
Yup, Lockheed's X-35 beat out a (horrendously ugly) Boeing airplane to win the contract, but my understanding was that the initial orders were cost-plus. That's pretty typical for large procurements of advanced aircraft. It's hard to know long it will take and how much it will cost to build something that bleeding-edge.
Except that if we custom-order a car, the manufacturer isn't legally prohibited from selling it to someone else if we end up refusing to buy it.